Drug solution density adjustment systems and methods

ABSTRACT

Devices, systems and methods for delivering one or more drugs to one or more internal body locations (such as the cerebrospinal fluid) are disclosed. In various aspects, the systems and methods may involve catheters having infusion sections with permeable membranes that develop significant back pressure to enhance uniform delivery of the drug over an infusion section; catheters that have two or more infusion sections spaced apart along the length of the same catheter, catheters that include two or more infusion sections serviced by independent lumens (such that, e.g., different drug solutions can be delivered to the different infusion sections); implantable drug delivery systems with pumps and multiple reservoirs from which drugs can be delivered; systems that are capable of delivering drug solutions with selected densities; etc.

RELATED APPLICATIONS

[0001] The present application claims the benefit under 35 U.S.C. Section 119(e) of U.S. Provisional Application No. 60/436,294 titled CATHETERS AND METHODS FOR THERAPEUTIC SUBSTANCE DELIVERY, filed on Dec. 23, 2002 and U.S. Provisional Application No. 60/508,353 titled CATHETERS AND METHODS FOR THERAPEUTIC SUBSTANCE DELIVERY, filed on Oct. 3, 2003, both of which are hereby incorporated by reference in their respective entireties.

BACKGROUND

[0002] There are a number of conventional devices available for delivering drugs to a patient. More specifically, completely implantable drug delivery systems are available. Examples include the ISOMED and SYNCHROMED implantable pumps available from Medtronic, Inc., Minneapolis, Minn. USA.

[0003] Completely implantable drug delivery systems typically include a pump which stores and infuses the drug in a desired infusion mode and rate, and a catheter which routes the drug from the infusion pump to the desired anatomic site. Implantable pumps may be large and are typically implanted in areas of the body with available volume that is not completely filled with body organs, such as the abdomen. The target site for drug infusion may, however, be located at a distance from the pump. A thin flexible catheter is typically implanted to provide a guided pathway for drugs from the pump to the target location.

[0004] Implantable pumps are often used to treat neurological diseases; examples are chronic pain and intractable spasticity. These conditions require treatment for a long time, frequently for the lifetime of the patient. An implantable pump can deliver drugs at a desired rate without intervention for a long time, and make drug therapy much easier and more accurate. Large doses of oral drugs would be required since the blood-brain barrier prevents most of the drug from reaching the central nervous system. Some of the drug that is blocked by the blood-brain barrier will instead travel to other organs, and can cause undesirable side effects. A catheter can, however, penetrate the membranes that comprise the blood-brain barrier and infuse the drug directly to the target receptors.

[0005] The neurological drug receptors for many therapies, such as pain and spasticity, are located in the spinal cord. A catheter cannot be surgically connected to the spinal cord because it could damage other neurons and cause serious neurological problems. The brain and spinal cord are surrounded by cerebrospinal fluid (CSF). CSF provides a cushioning effect for the spinal cord, but also provides a vehicle to deliver substances such as proteins, glucose, and ions (e.g. sodium, calcium, and potassium) to the central nervous system. Neurological drug infusion systems are designed to utilize this property of CSF. The drug is infused into CSF and then distributed through the CSF to the receptors in the spinal cord. These systems typically rely on infusion at one location.

[0006] Other limitations of known implantable systems and methods of drug delivery is that the systems may be limited to a single reservoir from which only one drug solution can be delivered at any given time. The density of the drug solutions delivered by such systems cannot be changed after implantation of the devices.

SUMMARY OF THE INVENTION

[0007] The present invention provides systems and methods for delivering one or more drugs to one or more internal body locations (such as the CSF). In various aspects, the systems and methods may involve catheters having infusion sections with permeable membranes that develop significant back pressure to enhance uniform delivery of the drug over an infusion section; catheters that have two or more infusion sections spaced apart along the length of the same catheter, catheters that include two or more infusion sections serviced by independent lumens (such that, e.g., different drug solutions can be delivered to the different infusion sections); implantable drug delivery systems with pumps and multiple reservoirs from which drugs can be delivered; systems that are capable of delivering drug solutions with selected densities; etc.

[0008] The present invention may, in one aspect, preferably provide physicians with the ability to tailor the delivery of drugs within the spinal region. Tailored delivery of one or more drugs in accordance with the present invention may, e.g., increase the therapeutic efficacy of the drug infused by the system and may also reduce the amount of drug that reaches other sites in, e.g., the spine or brain (thus potentially reducing undesirable side effects).

[0009] In accordance with various exemplary aspects of the invention, the distribution profile of an intrathecally delivered drug solution may be modified by, e.g., varying the baricity (density) of the solution, changing the concentration or hydrophilicity/hydrophobicity of the drug (e.g., selecting a polymorph form of an agent, acid or base salt or neutral form an agent, etc.; selecting a different suitable agent; etc.) or solution carrying the drug, changing the location within the spinal cord where the drug is infused, changing the infusion rate of the drug, changing a pore size of a permeable membrane through which the drug is infused, or a combination thereof.

[0010] In some embodiments, the present invention may be in the form of a drug delivery catheter that includes an elongated body with a proximal end and distal end. The catheter includes a lumen extending from the proximal end of the body to an infusion section spaced from the proximal end of the body. The infusion section may preferably include two or more openings in a wall of the lumen within the infusion section and a permeable membrane covering the two or more openings in the infusion section. The two or more openings and the permeable membrane covering them may preferably create a back pressure in the lumen such that the drug exits the infusion section through all of the two or more openings in the infusion section when a drug is delivered to the infusion section through the lumen at a continuous rate of 1 milliliter per hour or less.

[0011] In connection with the catheters described herein, it may be preferred that the permeable membrane create a back pressure of 300 pascals or more in the lumen when the drug is delivered to the infusion section through the lumen at a continuous rate of 2 microliters per hour.

[0012] An alternative manner of characterizing the permeable membrane of the catheter described in the preceding paragraph may be based on molecular weight cut-off, e.g., where the permeable membrane has a molecular weight cut-off of 80 kiloDaltons or less.

[0013] In other embodiments, a drug delivery catheter in accordance with the present invention may be described as including an elongated body having a proximal end and distal end. The elongated body includes a lumen extending from the proximal end of the body to an infusion section spaced from the proximal end of the body. The catheter may include one or more openings in a wall of the lumen within the infusion section and a permeable membrane covering the one or more openings in the infusion section. The one or more openings and the permeable membrane covering them may preferably create a back pressure of 300 pascals or more in the lumen when the drug is delivered to the infusion section through the lumen at a continuous rate of 2 microliters per hour. The permeable membrane may, e.g., have a molecular weight cut-off of 80 kiloDaltons or less.

[0014] In still another embodiment, a drug delivery catheter in accordance with the present invention may include an elongated body with a proximal end and distal end. A lumen may extend from the proximal end of the body to an infusion section spaced from the proximal end of the body. One or more openings may be formed in a wall of the lumen within the infusion section and a permeable membrane may cover the one or more openings in the infusion section. The permeable membrane may have a molecular weight cut-off of 80 kiloDaltons or less.

[0015] In other embodiments, the catheters described herein may be used in drug delivery systems that include a drug delivery apparatus including a pump and a reservoir. The drug delivery apparatus may preferably be implantable within the body of the patient.

[0016] Various methods of using drug delivery catheters including permeable membranes according to the present invention may also be characterized on the basis of back pressures developed at specified flow rates and/or the molecular weight cut-off of the permeable membrane. For example, delivering the drug may create sufficient back pressure in the lumen such that the drug passes through all of the two or more openings in the infusion section when the drug is delivered to the infusion section through the lumen at a continuous rate of 1 milliliter per hour or less. In addition, the method may be characterized as creating a back pressure of 300 pascals or more in the lumen when the drug is delivered to the infusion section through the lumen at a continuous rate of 2 microliters per hour.

[0017] In another method of using a drug delivery catheter according to the present invention, delivering the drug may involve creating a back pressure of 300 pascals or more in the lumen when the drug is delivered to the infusion section through the lumen at a continuous rate of 2 microliters per hour.

[0018] In still another method of using a drug delivery catheter according to the present invention, delivering the drug through the infusion section may involve passing the drug out of the infusion section through all of one or more openings formed through a wall of the lumen within the infusion section, wherein the drug passes through a permeable membrane covering the one or more openings, and wherein the permeable membrane has a molecular weight cut-off of 80 kiloDaltons or less.

[0019] In some embodiments, the drug delivery catheters used in, e.g., systems of the present invention may include more than one infusion section. The infusions sections may be located along the same lumen or different lumens. It may be preferred that the different infusion sections be separated along the axial length of the catheter by a distance of, e.g., 20 mm or more. Further, the walls of the lumen may preferably be impermeable to liquids between the infusion sections such that drug delivery through the catheter is restricted to the infusion sections.

[0020] Spacing between adjacent infusion sections along the length of a drug delivery catheter may be characterized in a variety of manners. As noted above, the infusion sections may preferably be separated by an axial distance of 20 mm or more. In other embodiments, the infusion sections may be separated by, e.g., an axial distance of one human vertebral level or more. In still other embodiments, the infusion sections may be separated by, e.g., an axial distance of 40 mm or more. In other embodiments, the infusion sections may be separated by, e.g., an axial distance that is a whole number multiple of one human vertebral level (e.g., 40 mm).

[0021] In other embodiments, the catheters including multiple infusion sections as described herein may be used in drug delivery systems that include a drug delivery apparatus including at least one pump and at least one reservoir. The drug delivery apparatus may preferably be implantable within the body of the patient. It may be preferred that the pump be an implantable pump and the reservoir be an implantable reservoir.

[0022] The present invention may also include a method of infusing a drug to multiple internal body locations by delivering a drug from a reservoir to a first infusion section and a second infusion section of a catheter through a lumen, wherein the catheter includes an elongated body comprising a proximal end and a distal end. The first infusion section and the second infusion section are located along the elongated body, with the second infusion section being located between the proximal end of the elongated body and the first infusion section. The first infusion section and the second infusion section may be spaced apart from each other along the elongated body by an axial distance of 20 mm or more. The method may further involve passing the drug out of the lumen through the one or more openings in the first infusion section and passing the drug out of the lumen through the one or more openings in the second infusion section.

[0023] In still other embodiments, the present invention may provide a drug delivery catheter having an elongated body with a proximal end and a distal end. A first lumen may extend from the proximal end of the body to a first infusion section located along the elongated body which may include one or more openings in the first lumen. The catheter may also include a second lumen extending from the proximal end of the body to a second infusion section that is located along the elongated body and that is spaced apart from the first infusion section along the body by an axial distance of 20 mm or more. The second infusion section may preferably be located along the elongated body between the proximal end of the elongated body and the first infusion section. The second infusion section may also include one or more openings in the second lumen within the second infusion section.

[0024] Spacing between adjacent infusion sections along the length of a drug delivery catheter including two or more lumens may be characterized in a variety of manners.

[0025] As noted above, the infusion sections may preferably be separated by an axial distance of 20 mm or more. In other embodiments, the infusion sections may be separated by, e.g., an axial distance of one human vertebral level or more. In still other embodiments, the infusion sections may be separated by, e.g., an axial distance of 40 mm or more. In other embodiments, the infusion sections may be separated by, e.g., an axial distance that is a whole number multiple of one human vertebral level (e.g., 40 mm).

[0026] In other embodiments, the catheters including multiple lumens, each with at least one infusion section as described herein may be used in drug delivery systems that include a drug delivery apparatus including at least one pump and at least one reservoir. The drug delivery apparatus may preferably be implantable within the body of the patient. It may be preferred that the pump be an implantable pump and the reservoir be an implantable reservoir.

[0027] The present invention may also preferably provide methods of delivering one or more drugs to two or more locations within the spinal region of a patient. Such a method may include delivering a first drug to a first location within the spinal region of a patient; and delivering a second drug to a second location within the spinal region of a patient; wherein the first drug and the second drug are the same or different. Delivery of the first and second drugs to the first and second locations may be performed simultaneously or not. Also, the first drug and the second drug may be delivered through the same catheter or different catheters. In some instances, the first drug may be delivered through a first lumen in a catheter and the second drug may be delivered through a second lumen in the same catheter. The catheters used in such a method may include, e.g., any suitable catheters among those described herein or other catheters that are not described herein.

[0028] The present invention may also include an implantable drug delivery system that includes an implantable pump assembly and two or more implantable reservoirs operably connected to the implantable pump assembly. The system also preferably includes a catheter connection port adapted to attach a catheter to the drug delivery system and a reservoir switching valve assembly between the two or more implantable reservoirs and the catheter connection port, wherein the two or more implantable reservoirs can be selectively connected to the catheter connection port. In some embodiments, the reservoir switching valve assembly may be optional and in such embodiments, it may be desirable to include a pump assembly that includes, e.g., two or more pump mechanisms.

[0029] Such implantable systems may include, e.g., in various embodiments: a telemetry module operably connected to control the reservoir switching valve assembly; an implantable density sensor; a telemetry module operably connected to the density sensor; means for mixing fluids delivered from at least two of the two or more reservoirs such that a mixed fluid having a selected density can be obtained based on, e.g., a density measured by the density sensor.

[0030] In such a system with multiple implanted reservoirs, two reservoirs of the two or more reservoirs contain different drugs that may, e.g., be in drug solutions having different densities. In another alternative, two reservoirs of the two or more reservoirs may contain the same drug in two different drug solutions having different densities.

[0031] Such a system may also incorporate means for modifying the flow rate to the catheter connection port such as by using an implantable pump assembly that includes at least one programmable pump mechanism, a flow restrictor, metering valve, etc.

[0032] In a system with multiple implanted reservoirs, it may be preferred to use a catheter that includes, e.g., a first lumen extending from the proximal end of the catheter to a first infusion section and a second lumen extending from the proximal end of the catheter to a second infusion section. Such a system may also preferably include a lumen switching valve assembly between the two or more reservoirs and the catheter, wherein the two or more reservoirs can be selectively connected to one or both of the first lumen and the second lumen.

[0033] In some embodiments, the system may include dedicated relationships between reservoirs and catheter lumens. For example, the two or more reservoirs may include a first reservoir connected to the first lumen of the catheter and a second reservoir connected to the second lumen of the catheter. Valves may be used to control flow through each of the lumens.

[0034] The present invention may also involve methods of delivering one or more drugs to at least one internal body location using a drug delivery system implanted in the body of a patient, wherein the drug delivery apparatus includes an implantable pump assembly, two or more implantable reservoirs operably connected to the implantable pump assembly, a catheter connection port adapted to attach a catheter to the drug delivery system, and a reservoir switching valve assembly between the two or more implantable reservoirs and the catheter connection port. The method may include, e.g., selectively connecting at least one reservoir of the two or more implantable reservoirs to the catheter connection port; and delivering a drug from at least one reservoir of the two or more implantable reservoirs to the catheter connection port using the implantable pump assembly.

[0035] In such a method, the reservoir switching valve assembly may be controlled from a location outside of the body of the patient. The method may involve, e.g., measuring density of the cerebrospinal fluid of a patient using an implanted density sensor.

[0036] In other variations, the methods may include mixing fluids delivered from at least two of the two or more reservoirs before delivering the drug. In some instances, the two reservoirs of the two or more reservoirs contain different drugs in solutions having the same or different densities. In still other instances, two reservoirs may contain the same drug in two different drug solutions having different densities.

[0037] In still other potential aspects of the present invention, the catheters and/or drug delivery systems may be used in methods of adjusting the density of a drug solution to be delivered to an internal body location of a patient. Such methods may involve, e.g., determining a selected density for the drug solution; formulating the drug solution from two or more components to obtain the selected density for the drug solution, and infusing the drug solution to an internal body location at a continuous rate of no more than 50 milliliters (ml) per hour for a period of five minutes or more. In variations on this method, the maximum infusion rate may be, e.g., no more than 25 ml per hour, no more than 10 ml per hour, no more than 5 ml per hour, or even potentially no more than 2 ml per hour. Variations may also be found in the time period over which the infusion is performed. The period of infusion may alternatively be, e.g., 10 minutes or more, one hour or more, eight hours or more, or even 24 hours or more.

[0038] In still other variations on the methods described in the previous paragraph, the infusing may preferably be performed for a period of at least 8 hours within a twenty four hour period. Alternatives to this may include, e.g., at least 12 hours within a twenty four hour period, or even at least 16 hours in a twenty four hour period.

[0039] In another manner of characterizing the invention, the infusion process may be described in terms of a duty cycle, e.g., where the infusion is performed for a duty cycle of at least 25% within a given time period, or at least 50% within a given time, or even at least 75% within a given time period. The time periods over which the duty cycle is determined may be, e.g., 8 hours or more, 12 hours or more, 16 hours or more, or even 24 hours or more.

[0040] In some methods, determining the selected density involves determining the density of the cerebrospinal fluid of a patient either in vivo (using a density sensor located within the cerebrospinal fluid of a patient) or measuring the density of the cerebrospinal fluid after removing the cerebrospinal fluid from the patient.

[0041] Formulating the drug solution may be performed outside of the body of the patient or within the body of the patient (using, e.g., some of the systems described herein). If the drug solution is formulated within the body of the patient, it may be desirable to obtain the components for the drug solution from two or more reservoirs implanted within the patient.

[0042] Because density variations can have an effect on the efficacy of a treatment plan, it may be desirable to obtain feedback regarding efficacy of the drug solution after delivering the drug solution to the patient. The method may then involve adjusting the density of the drug solution based on the feedback. The feedback may be provided by, e.g., the patient, doctors, nurses, other caregivers, sensors, etc.

[0043] In another method of adjusting the density of a drug solution, the present invention may involve determining a selected density for the drug solution; and controlling the temperature of the drug solution to increase or decrease the density of the drug solution to reach the selected density. As discussed above, determining the selected density may involve determining the density of the cerebrospinal fluid of a patient either in vivo (using a density sensor located within the cerebrospinal fluid of a patient) or measuring the density of the cerebrospinal fluid after removing the cerebrospinal fluid from the patient.

[0044] To take advantage of the use of drug solution density, it may be advantageous to employ a drug delivery system that includes a drug delivery apparatus with a pump assembly and two or more reservoirs operably connected to the pump assembly. The system may further include a catheter connection port adapted to attach a catheter to the drug delivery system and means for mixing fluids from at least two reservoirs of the two or more reservoirs at or before delivering the fluids to the catheter connection port.

[0045] Such a system designed to deliver drug solutions with selected densities may include, e.g., an implantable density sensor operably connected to the drug delivery apparatus.

[0046] In a system designed to supply drug solutions with selected densities, two reservoirs of the two or more reservoirs may preferably contain different fluids. The different fluids may, e.g., have different densities.

[0047] In one embodiment, a first reservoir of the two or more reservoirs may contain a first fluid with a low density, a second reservoir of the two or more reservoirs may contain a second fluid with an intermediate density, and a third reservoir may contain a third fluid with a high density (where the low, intermediate and high densities are relative to each other only). The second fluid may include the drug to be delivered such that addition of the first fluid lowers the density of the drug solution or addition of the third fluid increases the density of the drug solution. In some systems, the first fluid and the third fluid may be substantially free of the drug.

[0048] In another variation, at least two fluids of the first fluid, the second fluid, and the third fluid may include the same drug. In still another variation, two reservoirs of the two or more reservoirs may contain the same drug in two different drug solutions having different densities.

[0049] Density control systems may also include a thermal control device for controlling the temperature of the drug (in addition to controlling density through selective mixing of fluids having different densities).

[0050] It may be preferred that the pump assembly be an implantable pump assembly, and that the two or more reservoirs be implantable reservoirs operably connected to the implantable pump assembly, and further wherein the means for mixing is implantable means for mixing.

[0051] In another aspect, the present invention may provide a drug delivery system that includes a drug delivery apparatus having a pump assembly, one or more reservoirs operably connected to the pump assembly, and a catheter connection port adapted to attach a catheter to the drug delivery system. The system also includes a thermal control device for controlling the temperature of the drug delivered to the patient.

[0052] The thermal control device may, e.g., control the temperature of the drug before the drug is delivered to the catheter connection port. Alternatively, the thermal control device may control the temperature of the drug after the drug passes through the catheter connection port. The thermal control device may be located within a catheter connected to the catheter connection port. Such a system may also include an implantable density sensor operably connected to the drug delivery apparatus. The density sensor may be operably connected to the drug delivery apparatus, whereby a fluid having a selected temperature can be obtained based on a density measured by the density sensor. Such a system may preferably be implantable.

[0053] These and other features and advantages of the systems and methods of the present invention may be described below in connection with some illustrative examples of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0054]FIG. 1A is a schematic diagram of one drug delivery system implanted within the body of a patient and infusing drug into the brain.

[0055]FIG. 1B is a schematic diagram of one implanted drug delivery system for infusing drug directly to the spinal region.

[0056]FIG. 1C is a schematic diagram of one implanted drug delivery system for infusing drug directly to the peripheral nervous system.

[0057]FIG. 2 depicts an enlarged view of a drug delivery system similar to that depicted in, e.g., FIG. 1B.

[0058]FIG. 3 depicts the distal end of the catheter of FIG. 2 infusing drug into the spinal region.

[0059]FIG. 4 is an enlarged cross-sectional view of one example of an infusion section including multiple infusion openings in a catheter used in connection with the present invention.

[0060]FIG. 5 is an enlarged cross-sectional view of another example of an infusion section including a permeable membrane in a catheter used in connection with the present invention.

[0061]FIG. 6 depicts a catheter including two infusion sections spaced apart along the axial length of the catheter.

[0062]FIG. 7 depicts another drug infusion system according to the present invention including a catheter with two lumens and two pump mechanisms.

[0063]FIG. 8 is a schematic diagram of another drug delivery system according to the present invention including multiple reservoirs for mixing drug solutions with selected densities or other properties.

[0064]FIG. 9 is a schematic diagram of another drug delivery system including thermal control devices for controlling the temperature of the drugs delivered to the patient.

[0065]FIG. 10 is a schematic diagram of another drug delivery system according to the present invention incorporating a variety of optional components.

[0066]FIG. 11 is a schematic diagram of another drug delivery system according to the present invention incorporating a lumen switching valve assembly.

[0067]FIG. 12 depicts a catheter according to the present invention including a fork and two branches extending therefrom.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE INVENTION

[0068] In the following detailed description of illustrative embodiments of the invention, reference is made to the accompanying figures of the drawing which form a part hereof, and in which are shown, by way of illustration, specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.

[0069] The present invention may be used in connection with a variety of methods, catheters and/or systems as may be described in, e.g., U.S. patent application Ser. No. ______, titled REDUCTION OF INFLAMMATORY MASS WITH SPINAL CATHETERS, filed on even date herewith (Attorney Docket No. P-10333.00); U.S. patent application Ser. No. ______, titled METHOD OF DELIVERING DRUGS TO SPECIFIC REGIONS OF THE SPINAL CORD, filed on even date herewith (Attorney Docket No. P-10781); U.S. patent application Ser. No. ______, titled TRIALING SYSTEMS FOR EVALUATION OF THE EFFICACY OF TREATMENT, filed on even date herewith (Attorney Docket No. P-10785.00); and U.S. patent application Ser. No. ______, titled METHOD OF DELIVERING DRUG TO BRAIN VIA THE SPINAL CANAL, filed on even date herewith (Attorney Docket No. P-10783.00).

[0070] The present invention relates to the delivery of drugs. For the purposes of the present invention, the term “drug” means any pharmacological or therapeutic agent or combination of agents delivered to provide therapy to a patient (human or non-human animals). The drugs will typically be liquids or materials contained in liquid carriers as either solutions or mixtures (although where used herein, the term “solution” refers to both solutions and mixtures).

[0071] Furthermore, although in many instances, the catheters, drug delivery systems, methods and other aspects of the invention may be useful in connection with delivery of one or more drugs to the spinal region, it should be understood that the present invention may find use in connection with delivery of one or more drugs to other internal body locations as well, including, but not limited to, the brain or any other suitable anatomical location.

[0072] As used herein, the term “spinal region” includes the spinal canal (including the spinal cord, intrathecal space, dura, epidural space, etc.), vertebra, spinal discs, nerve roots, and the ligaments, tendons and muscles in between and surrounding the vertebra.

[0073] Exemplary embodiments of some drug delivery systems for infusing drugs are depicted in FIGS. 1A, 1B, and 1C. FIG. 1A is a schematic diagram of a drug delivery system for infusing drug to the brain, FIG. 1B is a schematic diagram of a drug delivery system for infusing drug to the spinal region, and FIG. 1C is a schematic depiction of a drug delivery system for infusing drug to the peripheral nervous system.

[0074] The drug delivery systems depicted in FIGS. 1A and 1B includes a drug infusion pump assembly 10A/10B and catheter 20A/20B having a proximal end 22A/22B attached to the pump assembly and distal end 24A/24B implanted within the patient. The distal end 24A is implanted within the brain of the patient, while the distal end 24B is implanted within the spinal column 30 of the patient.

[0075]FIG. 1C depicts only a portion of the drug delivery system, namely the portion of catheter 20C including its distal end 24B, which is implanted to infuse drugs to the peripheral nervous system. The depicted infusion site in the arm is provided as exemplary only, with the systems of the present invention capable of infusing drugs to any internal body location.

[0076] Furthermore, although the systems of FIGS. 1A, 1B, and 1C are depicted infusing drugs into only one area, e.g., brain, spinal region or peripheral nervous system, it should be understood that a single system could infuse one or more drugs to one or more locations in any one or more of the brain, spinal region and/or peripheral nervous system. Also, although depicted in connection with a human body, it should be understood that the drug delivery systems of the present invention could also be used on non-human animals.

[0077] The pump assembly 10 may preferably be surgically implanted subcutaneously in the pectoral or abdominal region of the subject's body. The pump assembly 10 may be any suitable mechanism capable of delivering one or more drugs to a patient. The pump assembly 10 preferably includes a pumping mechanism, at least one reservoir containing the drug to be delivered, and a power supply to operate the pump assembly 10 such that the drug is delivered to the patient at a selected rate. Examples of some suitable pumps may include, e.g., commercially available implantable infusion pumps such as, for example, the SYNCHROMED EL pumps, Models 8626 and 8627, manufactured by Medtronic, Inc., Minneapolis, Minn. It should be understood that some pumps used in connection with the present invention may not require a separate power supply.

[0078] While an implantable pump assembly 10 is depicted, it should be understood to those skilled in the art that the device used to deliver drug to the catheter may be either implanted or extracorporeal. As used herein, the term “implantable” means that the system, apparatus or device is adapted for implantation in the body of subject where it is located at feast subcutaneously.

[0079] One exemplary structure of a pump assembly 10 and catheter 20 may be understood by reference to FIG. 2, which depicts one embodiment of the system with a portion of the catheter 20 shown in an enlarged half section. The size of the catheter 20 is exaggerated for ease of illustration of the structure thereof and the full length of the catheter 20 is not shown for simplicity of illustration. The proximal end 22 of the catheter 20 is coupled to the pump connector 12. The connection between the catheter 20 and the pump connector 12 is shown schematically in FIG. 2. It should be understood that the actual type of connection between the pump connector 12 and the catheter 20 will vary depending upon the particular type of pump assembly 10 utilized.

[0080] The catheter 20 includes an elongated tubular portion 23 that preferably extends from the proximal end 22 to the distal end 24. The catheter 20 depicted in FIG. 2 includes a lumen 26 that terminates at opening 28 at the distal end 24. Drug delivered from the pump assembly 10 to the catheter 20 passes through lumen 26 and exits the catheter through opening 28.

[0081] When implanted for delivering drugs to, e.g., the spinal region, it may be preferred that at least a portion of the catheter 20 be located within the CSF of the patient such that as drug exits the catheter 20 it enters directly into the CSF. By “directly,” it is meant that the drug preferably does not contact other tissues or bodily fluids before reaching the CSF of the patient.

[0082] The body of catheter 20 may preferably be constructed of any suitable material, e.g., an elastomeric tube. If used in the spinal canal, the catheter 20 may be floating free in the CSF and may contact the spinal cord. As a result, in such an application the catheter 20 may preferably be soft and flexible to limit any chance of damaging the spinal cord. Examples of some suitable materials include, but are not limited to, silicone rubber (e.g., polydimethyl siloxane) or polyurethane, both of which can provide good mechanical properties and are very flexible. Suitable materials for the catheter 20 are also preferably chemically inert such that they will not interact with drugs or body tissue or body fluids over a long time period.

[0083] In some embodiments, the catheter may preferably be sized to fit in the gap between the spinal cord 32 and the dura 36 (see, e.g., FIG. 3). The inside diameter, e.g., the diameter of the lumen 26, is preferably large enough to accommodate expected infusion rates with acceptable flow resistance. The wall 21 of the catheter 20 is preferably thick enough to withstand normal handling during the implant procedure and forces from body tissues during normal motion. As an example, the catheter 20 may have an outside diameter of 1.25 millimeters (mm) and an inside diameter of 0.5 mm, with a wall thickness of 0.375 mm. The catheter 20 may be, e.g., 50 centimeters (cm) long to reach from, e.g., a drug infusion pump implanted in the patient's abdomen to the spine.

[0084]FIG. 3 depicts catheter 20 positioned within a schematic representation of a spinal canal 30. The spinal canal 30 includes the spinal column 32 which terminates at the cauda equina 34. Also depicted is the dura 36 which contains the cerebrospinal fluid (CSF) that surrounds the spinal column 32. The catheter 20 is positioned such that the distal end 24 of the catheter 20 is located within the volume occupied by the CSF.

[0085] In the embodiment depicted in FIGS. 2 & 3, the catheter 20 includes only one opening 28 at the distal end 24 of the catheter 20. As a result, drugs delivered to the CSF through catheter 20 will exit through the opening 28 in the distal end 24 of the catheter 20. If the density of the drug so delivered is lighter than the CSF into which the drug is delivered, then the drug may form a plume 40 as seen in FIG. 3 in which the drug rises from the delivery point.

[0086] Many alternatives may be provided for the structure through which the drug passes out of the catheter. The catheter 20 including an opening 28 at its distal end 24 is only one example. FIG. 4 depicts a section of one alternative design in which the catheter 120 includes multiple openings 128 formed through the wall of the catheter 120 within an infusion section 127. As drug moves through the lumen of the catheter 120, it exits through the openings 128. In such an embodiment, it may be preferred that the distal end of the catheter 120 be closed such that the drug exits through openings 128 in the catheter wall. The size and spacing of the openings 128 may vary depending on a variety of factors such as, e.g., viscosity of the drug being delivered, desired delivery rate, etc.

[0087] The axial length of the infusion section 127 (as measured along an axis extending from the proximal to the distal end of the catheter) may be selected based on a variety of factors. For example, to control pain, the pain signals can be blocked by appropriate analgesic drugs in the dorsal nerve roots or in the spinal cord. Nerve roots do not have a single junction with nerve cells in the spinal cord, but split into many branches in both directions. To block a substantial number of pain signals, the drug may preferably be delivered over several vertebral levels above and below the affected nerve root. As an example, the infusion section may be constructed to cover three vertebral levels, e.g., the affected nerve root entry level and one vertebral level above and below. Each vertebral segment in a human adult is approximately 40 mm long, and, as a result, the infusion section could be, e.g., 80 mm long.

[0088] The length of infusion section 127 over which the openings 128 are dispersed may, in some embodiments, preferably have a limited axial length of, e.g., 320 millimeters (mm) or less, in some instances 160 mm or less, or even 120 mm or less. At the lower end of the range, it may be preferred that the infusion section 127 have an axial length of 20 mm or more, possibly 40 mm or more.

[0089]FIG. 5 depicts another potential construction for the infusion section 227 of a catheter 220 in an enlarged cross-sectional view. The depicted infusion section 227 includes openings 228 formed in the lumen 226, e.g., through the wall 221 of the catheter 220. The distal end 224 of the catheter 220 may preferably include a plug 229 or be closed in some other manner.

[0090] Unlike catheter 120 depicted in FIG. 4, infusion section 227 of catheter 220 includes a permeable membrane 225 through which any drugs passing out of catheter 220 must pass. The permeable membrane 225 may be provided as seen in FIG. 5, e.g., as a hollow tube located within lumen 226 of the catheter 220 that is positioned to cover openings 228 such that any drug must pass through the permeable membrane before passing through openings 228. Alternative constructions could include a permeable membrane over the outside of the catheter or plugs of a permeable membrane located within the openings themselves.

[0091] In the depicted configuration, the tubing of the catheter 220 may preferably provide mechanical support for the permeable membrane 225 and may also preferably provide protection from damage for the permeable membrane 225.

[0092] The permeable membrane 225 may preferably be provided in the form of a hollow fiber similar to those used in, e.g., blood oxygenators or kidney dialysis systems. Hollow fiber permeable membranes may be made from a number of different materials that preferably do not chemically interact with the drugs to be delivered and are biocompatible, e.g., polyurethane, silicone rubber, polyimide, polyethylene, polysulfone, or polyethersulfone.

[0093] In the depicted embodiment, the outside diameter of the hollow fiber permeable membrane 225 may be the same as the inside diameter of the catheter lumen 226 such that the permeable membrane 225 may be retained in the selected location by friction. Alternatively, the permeable membrane 225 may be held in place by any other suitable technique or techniques, e.g., adhesives, thermal welding, chemical welding, etc. Furthermore, although the depicted permeable membrane 225 is provided in the form of a hollow fiber, the permeable membrane 225 may be provided in any other suitable form, e.g., a plug occupying the lumen 226, sheet, etc.

[0094] The openings 228 within the infusion section may be arranged in any desired manner, e.g., linearly along the axis of the catheter 220, in a spiral around the axis, a series of circumferential circles, etc. Locating the openings 228 on one side of the catheter 220 may be beneficial in, e.g., distributing the drug as described herein. As one example, the infusion openings may be, e.g., 0.05 mm in diameter, with, e.g., ten to twenty holes distributed over the infusion section 227.

[0095] As compared to spinal catheters with one or multiple infusion openings as depicted in FIGS. 2 and 4, a spinal catheter 220 having a permeable membrane 225 may offer a number of potential advantages. For example, if the pump used to deliver drug through a catheter having an infusion section with multiple holes and no permeable membrane is programmed to deliver the drug at a low rate (e.g., 0.5 milliliters (ml) per day), the drug may exit only through a single infusion opening, typically the opening that is closest to the pump. This may occur because the infusion openings are so large that no back pressure is built up in the catheter at the low infusion rates to force the infusate to reach all of the holes.

[0096] If, however, a permeable membrane 225 with sufficiently small pore sizes is used, a back pressure of drug may be built up in the catheter lumen 226 that is large enough to distribute the drug over the entire length of the infusion section 227 such that the drug passes through all of the openings 228 in the infusion section 227.

[0097] In one manner of characterizing some catheters of the present invention, the openings 228 and the permeable membrane 225 covering them within the infusion section 227 may preferably create a back pressure in the lumen 226 such that the drug exits the permeable membrane 225 through all of the openings 228 in the infusion section 227 when a drug is delivered to the infusion section through the lumen 226 at a continuous rate of 1 milliliter per hour or less.

[0098] In another manner of characterizing some catheters of the present invention, the openings 228 and the permeable membrane 225 covering them within the infusion section 227 may preferably create a back pressure 300 pascals or more in the lumen when the drug is delivered to the infusion section through the lumen at a continuous rate of 2 microliters per hour. Even at such a low back pressure, the permeable membrane 225 may preferably cause the drug to pas through all of the openings within the infusion section 227 to enhance uniform delivery of the drug over the infusion section 227.

[0099] The permeable membrane (whether in the form of a hollow fiber or some other shape) may be provided with a variety of pore sizes. The membrane pore size may be characterized in terms of Molecular Weight Cutoff (MWCO), typically the largest size molecule that will pass through the membrane. More specifically, MWCO of a permeable membrane refers to a membrane through which 90% of a substance having a particular molecular weight can pass under certain test conditions. That is, a membrane through which 90% of a permeate having a molecular weight of 80 kDa passes would be determined to have a MWCO of 80 kDa. Permeates useful for determining molecular weight cutoff include dextran T-fractions and albumin. The amount of permeate that passes through a membrane may be determined by comparing HPLC data regarding a solution containing the permeate before being applied to the membrane and after passing the membrane. HPLC analysis is useful because a calibration curve of elution time versus molecular mass may be produced. Thus, the amount and molecular weight of permeate passing through the membrane may be determined by comparison to the calibration curve. This method of measurement is typically used by filter manufacturers for filter pore sizes smaller than 0.1 micrometer (μm). In connection with the present invention, it has been found experimentally that a permeable membrane with a molecular weight cutoff of 80,000 Daltons or less may preferably be used to achieve the desired infusion characteristics.

[0100] When characterized in terms of back pressure developed within the lumen, it may be preferred that the back pressures and/or flow rates are for drug solutions that may preferably have, e.g., a viscosity of water or higher at, e.g., basal body temperatures or the temperatures at which the drug solutions are delivered.

[0101] In addition to generating the desired back pressure, permeable membranes with these pore sizes may preferably cause the drug exiting the catheter to form droplets that may preferably be small enough to be rapidly diluted into, e.g., CSF and form a diffuse cloud at the infusion site. Suitable hollow fiber permeable membranes may be obtained from, e.g., Minntech Corporation (Minneapolis, Minn.), Spectrum Laboratories, Inc. (Rancho Dominguez, Calif., Membrana GmbH (Wuppertal, Germany), etc.

[0102] One method of manufacturing a catheter 220 with an infusion section 227 including a hollow fiber permeable membrane 225 as seen in, e.g., FIG. 5 may involve inserting the hollow fiber permeable membrane 225 in the lumen 226 of the catheter 220 and retaining the membrane 225 in position with friction. In one method of providing a friction fit, the hollow fiber 225 may have an outside diameter that is slightly larger than the inside diameter of the lumen 226, e.g., the hollow fiber 225 may have an outside diameter of 0.6 mm to fit inside a lumen with an inside diameter of 0.5 mm. If the catheter 220 is manufactured of, e.g., silicone, polyurethane, etc., the lumen 226 may be temporarily swelled by soaking in, e.g., ethyl alcohol. While the lumen 226 is swollen, the hollow fiber 225 may be placed in the lumen 226. As the alcohol evaporates out of the tubing used for catheter 220, the tubing will shrink to its original dimensions, preferably holding the hollow fiber permeable membrane 225 in position by frictional forces.

[0103] Another optional feature that may be provided in connection with the present invention is depicted in the cross-sectional view of FIG. 6. The catheter 320 includes two separate infusion sections 327 a and 327 b (collectively referred to herein as “infusion sections 327”) spaced apart from each other along the axial length of the catheter 320. As discussed herein, the spacing between separate infusion sections is measured between the ends of the infusion sections 327 a and 327 b. In the case of infusion sections that include openings such as depicted in FIG. 6, the ends of the infusion sections are determined by the openings 328 in the two different infusion sections. For example, the spacing of the infusion sections 327 a and 327 b in FIG. 6 would be determined by the lowermost opening 328 in infusion section 327 a and the uppermost opening 328 in infusion section 327 b. It may be preferred that the lumen is impermeable to liquids between any successive pair of infusion sections such as infusion sections 327.

[0104] It should be noted that catheters according to the present invention that include two or more infusion sections may preferably include at least two such infusion sections, e.g., infusion sections 327, along one axial length of an elongate body as seen in FIG. 6 such that at least one infusion section is located between another infusion section and the proximal end of the body on which the infusion sections are located. This is in contrast to, e.g., previously known branched catheters in which each branch contains one infusion section, such that any one of the axial lengths defined by such a catheter includes only one infusion section (see, e.g., International Publication No. WO 02/07810 A2 (Elsberry et al.)) with no infusion sections located between the proximal end of the catheter and another infusion section.

[0105] The axial distance between the different infusion sections 327 may be selected based on a variety of factors such as, e.g., the distance between anatomical features to which a drug is to be delivered. For example, it may be preferred that the infusion sections 327 be separated by the distance of one human vertebral segment (e.g., 40 mm) or more. In some instances, it may be preferred that the infusion sections be spaced apart from each other by an axial distance that is a whole number multiple of one average human vertebral level (e.g., 40 mm).

[0106] Each of the infusion sections 327 may preferably include a permeable membrane 325 and one or more infusion openings 328. Because the infusion sections 327 are displaced from each other, it may be preferred to use separate permeable membranes 325 in each of the infusion sections 327. The separate permeable membranes 325 may have the same or different physical properties (e.g., MWCO values, materials, etc.) In some instances, however, a single unitary permeable membrane may extend between different infusion sections 327. Also, although FIG. 6 depicts only two infusion sections 327, it will be understood that catheters of the present invention may include more than two separate infusion sections, e.g., three or more infusion sections.

[0107] As for one potential use for a catheter having more than one infusion section, a patient may have chronic pain symptoms from more than one cause or in more than one location. For such a patient, it may be desirable to deliver analgesic drugs in more than one location along the spinal cord to reach all appropriate synapses. For example, one infusion section could be located proximate the spinal cord at a higher vertebral level, so that the drug will preferably diffuse to the dorsal horn.

[0108] Still another drug delivery system that may be used in connection with the present invention is depicted in FIG. 7. The catheter 420 (depicted in cross-section) includes two infusion sections 427 a and 427 b (collectively referred to herein as “infusion sections 427”). Unlike catheter 320 of FIG. 6 in which a single lumen services both infusion sections 327, however, each of the infusions sections 427 of catheter 420 is serviced by a separate lumen 426 a or 426 b.

[0109] Even though serviced by separate lumens 426 a and 426 b, however, the infusion sections 427 can still be characterized as including one section 427 b that is located between the proximal end of the catheter 420 (i.e., the end attached to pump assembly 410) and the other infusion section 427 b along the axial length of the body of the catheter 420.

[0110] In such an embodiment, the catheter 420 may be used to, e.g., deliver two different drugs to different locations along the length of the catheter 420 (the different locations being identified by the location of the different infusion sections 427). Alternatively, the catheter 420 may be used to deliver the same drug to two different locations at different times and/or for different periods of time. It will be understood that although only two lumens and infusion sections are depicted, devices and methods of the present invention may involve catheters with three or more lumens, three or more infusion sections and associated and pump assemblies.

[0111] Also, although two infusion sections 427 and two lumens 426 a and 426 b are depicted in connection with the embodiment of FIG. 7, it will be understood that catheters of the present invention may include more than two infusion sections and/or more than two lumens to service the different infusion sections. Although not depicted, for example, one (or both) of the infusion sections 427 could be serviced by two or more separate lumens such that two or more different drugs could be delivered by the same infusion section at the same or different times. For example, infusion section 427 a could be serviced by two lumens in place of the single lumen 426 a depicted in FIG. 7.

[0112] A schematic diagram of one pump assembly 410 that may be used in connection with a catheter 420 is seen in FIG. 7. The pump assembly 410 may include, e.g., multiple pump mechanisms 410 a and 410 b that are, respectively, preferably connected to lumens 426 a and 426 b. Such a system may be useful if the two different pump mechanisms 410 a and 410 b are to be operated independent of each other. In some other systems, it may be sufficient to provide a single pump mechanism including two or more reservoirs with different drug solutions. In such a system, the reservoirs may be dedicated to a particular lumen or a switching valve assembly may be used to deliver drug solution from either reservoir to either or both of the lumens 426 a and 426 b as desired.

[0113] Among the methods of the present invention, it may be beneficial to exploit the natural tendencies of liquids to move relative to each other in response to gravitational and other forces. For example, because humans sit and stand in an upright position when awake, drugs delivered to the CSF may rise or fall in the spinal canal due to buoyancy. Buoyant forces may move the drug more rapidly than diffusion processes cause the drug to spread radially. Drugs that are more dense than CSF may tend to fall (i.e., move towards the cauda equina) and drugs that are less dense than CSF will rise (towards, e.g., the brain). Density of fluids may be described in terms of baricity. Drugs (or solutions carrying the drugs) may be described relative to the CSF of a patient as being hypobaric (e.g., less dense than CSF and, therefore, tending to rise in CSF) or hyperbaric (e.g., more dense than CSF and, therefore, tending to fall in CSF). The drug may also be described as isobaric (e.g., have neutral baricity, i.e., the same density as CSF) and, therefore, neither tending to rise or fall within the CSF.

[0114] Thus, if a patient is not responding to a particular therapy because a catheter is delivering a drug to a location that is too high in the spinal column, a drug solution having an increased density may be introduced to allow the drug to drop to a level of the spinal column where the drug may be more effective in treating the patient. If a patient is not responding to a particular therapy because a catheter is placed too low in the spinal column, a drug solution having decreased density may be introduced to allow the drug to rise to a level of the spinal column where the drug may be more effective in treating the patient. The catheter may also be repositioned to more effectively deliver the drug to a more desired region of the spinal cord.

[0115] If it is desired to have a drug reach a selected region of a spinal cord in roughly proportional concentrations across the particular region, it may be desirable to infuse the drug through a permeable membrane such that the drug may readily mix with CSF and diffuse throughout the particular region in roughly equal concentrations.

[0116] In some methods according to the present invention, the density of the drug solution may be adjusted before the drug solution is delivered to the pump apparatus. In such a system the density of the patient's CSF may be known (within a range of biologically expected values) or the actual density of the CSF may be determined by, e.g., drawing a sample and determining the density of the sample. The density of the drug solution may be adjusted relative to the expected or measured density of the CSF and a drug solution with a selected density can be supplied in the pump apparatus for delivery to the CSF by infusion.

[0117] In a variation on the above example, a system may be supplied that includes the same drug in two or more different solutions that have different densities relative to the density of the CSF. Referring to, e.g., FIG. 7, the two pump mechanisms 410 a and 410 b may be loaded with the same drug in solutions having two different densities. As a result, the same drug may be delivered to the CSF with different densities based on, e.g., the measured density of the patient's CSF, a desired distribution profile, etc. The different drug solutions may be delivered to either of the infusion sections 427 a and/or 427 b as desired.

[0118] In one variation on this method, different drug solutions with same or different densities may also be supplied in the reservoirs of each of the different pump mechanisms 410 a and 410 b. For example, it may be desirable to use more than one analgesic drug to treat multiple types of pain. For example, nociceptive pain, caused by stimulation of neurosensors, will typically respond to an opioid such as morphine, but neuropathic pain caused by damage to nerve cells will typically respond better to a local anesthetic such as BUPIVACAINE. One method of combining more than one drug is to simply mix them in the reservoir of an implantable drug pump and infuse the mixture through a catheter.

[0119] In some cases, however, it may be preferred to deliver the different drugs separately to different locations. The system of FIG. 7 may be used to accomplish this method because catheter 420 has two separate lumens 426 a and 426 b and separate infusion sections 427 a and 427 b at different locations on the catheter 420. For example, BUPIVACAINE could be infused through the first lumen 426 a such that it is infused proximate the lumbar nerve roots. A second drug, e.g. morphine, may be infused through the second lumen 426 b at, e.g., a location proximate the spinal cord at a higher vertebral level, so that the drug will preferably diffuse to the dorsal horn the dorsal horn which is at a higher, thoracic level in the spinal canal.

[0120] Although it may be beneficial to use a system in which one or more drug solutions are formulated outside of the patient to have a selected density, it may be beneficial to mix or formulate drug solutions having selected densities on-board the pump assembly. By mixing the drug solutions on-board the pump assembly (which may preferably be implanted in the body of the patient), a level of control may be achieved that is not possible in known systems.

[0121] One exemplary pump assembly 510 that may be used in connection with the present invention to take advantage of the buoyant forces to achieve some desired drug distribution profile is depicted in FIG. 8 (as a schematic block diagram for simplicity). The pump apparatus 510 includes a connector 512 for connection to a catheter 520. The catheter 520 may preferably include one or more lumens that each feed one or more infusion sections 527 a and 527 b as discussed herein.

[0122] The depicted pump apparatus 510 includes multiple reservoirs 514, 515, 516, 517, and 518. The reservoirs 514, 515, 516, 517, and 518 may contain the same fluids or different fluids, although it may be preferred that at least one of the reservoirs contain at least one drug for delivery to the patient. The other reservoirs may contain fluids that are designed to allow the user to manipulate the density of the drug solution delivered through the catheter. For example, reservoir 515 may contain a hypobaric liquid (e.g., water), reservoir 516 may contain a hyperbaric liquid (e.g., glucose solution), and reservoir 517 may contain a neutral liquid (e.g., saline). When combined with, e.g., a first drug in reservoir 514 in various fractions, the density of the drug solution delivered through the catheter 520 can be adjusted to achieve a desired density or baricity with respect to the CSF. Similarly, reservoir 518 may include, e.g., a second drug that may also be delivered to the catheter 520 in selected densities. In still other variations, two or more of the reservoirs may contain the same drug, but in solutions having different densities.

[0123] The depicted pump apparatus 510 includes optional means for mixing 513 a and 513 b to mix the various components of the drug solutions before delivery to the connector 512 and attached catheter 520. The means for mixing 513 a and 513 b may be provided in a variety of forms, e.g., as mixing chambers, mechanical agitators, vibrating components, static mixers, etc, and combinations thereof. In another alternative, the velocity at which the components are delivered to, e.g., the means for mixing 513 a and 513 b, the connector 512, and/or the catheter 520 may be increased to enhance mixing. Furthermore, the means for mixing may be incorporated into the catheter 520 itself.

[0124] Each of the reservoirs may also preferably be operably connected to a refilling port 514 p, 515 p, 516 p, 517 p, and 518 p such that the different reservoirs can be refilled. The ports may be located in one common septum or in different septums at different locations on the body of the pump apparatus. A variety of techniques may be used to ensure refilling of the selected reservoir. For example, the ports may accept differently sized or shaped needles, the ports may be located in known positions and a template may be placed on the patient's skin to assist in refilling, etc.

[0125] By providing a variety of drugs and liquids as in pump apparatus 510, the density of the drug solutions delivered to the CSF may be adjusted to, e.g., mix a drug solution that is isobaric (i.e., neutral density) with respect to the CSF, mix a drug solution that is hyperbaric (i.e., less dense) as compared to the CSF, and mix a drug solution that is hypobaric (i.e., more dense) as compared to the CSF. Furthermore, the density of the drug solution can be adjusted during delivery, i.e., it may be changed to adjust to changes in the density of the CSF and/or to achieve a desired density profile. For example, a hyperbaric drug solution may be delivered followed by delivery of a hypobaric drug solution (or vice versa) to deliver drug over a wider region of the spinal canal.

[0126] Where the pump apparatus 510 includes two different drugs, it will be understood that a similar system could be provided that includes only one drug. Other variations may be provided in catheter 520 which may include, e.g., one or more lumens, one or more infusion sections, etc.

[0127] One optional feature that is depicted in connection with FIG. 8 is that catheter 520 may include a density sensor 550 such that the actual density of the CSF may be measured. Density sensors may be manufactured using, e.g., microelectromechanical sensor (MEMS) technology in the form of a beam or float configuration. See, e.g., Costello et al., “Density and Viscosity Sensing with Ultrasonic Flexural Plate Waves,” Proceedings of Transducers '93, 7^(th) International Conference on Solid-State Sensors and Actuators, Yokohama, Japan, June 1993, Institute of Electrical Engineers, Japan, pp. 704-707. Such devices may be incorporated in the delivery catheter 520 as depicted or, alternatively, a separate device may be located in the CSF to measure CSF density.

[0128] If the actual density of the CSF is measured, that information can be fed back into the pump assembly 510 such that the formulation of the drug solution or solutions can be adjusted to achieve a desired density relative to the CSF density. Such measurements and/or adjustments may be made continuously or at different times as desired using, e.g., open loop or closed loop control systems and methods.

[0129] In spite of the density of the drugs as discussed above, drugs may be delivered to the CSF in a manner that results in essentially neutral buoyancy even though the drug itself may be hypobaric or hyperbaric with respect to CSF. For example, if a permeable membrane is used to deliver the drug, the droplets or particles of drug exiting from the membrane may be so small as to result in a drug-CSF mixture that has a density close to pure CSF, thus reducing buoyant forces on the drug. The drug may then remain in the area of infusion, and diffusion will expand the drug into a cloud radially.

[0130] It should also be understood that although buoyant forces may play a role in drug movement and/or diffusion, the CSF itself is undergoing oscillation and bulk flow that may sometimes overcome the effects of baricity, e.g., causing hyperbaric drugs to rise and/or hypobaric drugs to fall in the spinal column.

[0131] Other factors that may play a role in the diffusion of drugs within the spinal canal include, e.g., the rate of infusion, drug distribution patterns between the different compartments of the spinal canal, whether the drugs are hydrophilic or lipophilic, the temperature of the drug at the time of infusion, etc.

[0132] With respect to the rate of infusion, low rates of infusion may tend to yield more equitable drug distribution radially for both hypobaric and hyperbaric drugs. Faster flow rates may lead to broader drug distribution over more vertebral segments than slower flow rates. As such, if it is desirable to reach a variety of levels of a spinal column with drug, the flow rate with which the drug is delivered may be increased. In such circumstances, it may be desirable to decrease the concentration of a drug to be delivered. If it is desired to have a drug localized to a region around a particular level of the spinal column, the flow rate with which the drug is delivered may be decreased. In such circumstances it may be desirable to increase the concentration of the drug within the solution delivered through the catheter.

[0133] It may also be desirable to infuse a drug in discrete intervals in which a bolus of drug is delivered followed by an interval in which little or no drug is delivered through the catheter (as opposed to a continuous delivery infusion). Such non-continuous delivery modes may also be useful to modify the distribution profile of a drug within the spinal column.

[0134] In addition, bolus or non-continuous delivery of a drug may provide other advantages in the management of the body's response to infusion of a drug. For example, such a delivery method may be helpful in reducing the incidence of inflammatory masses at the infusion site. In particular, the systems and methods of the present invention may be helpful in addressing this issue because the site at which the drug is delivered may be periodically changed (using, e.g., multiple infusion sites). In addition, by adjusting the density of the drug solution, various distribution profiles for the infused drug may be obtained that could reduce the incidence of inflammatory masses (e.g., alternating between hypobaric and hyperbaric drug solutions). Also, using systems that deliver two or more different drugs may also be used to address the incidence of inflammatory masses by alternating delivery between the different drugs to ameliorate the inflammatory response to continuous delivery of the same drug. Still another manner by which the catheters, systems and methods of the present invention may reduce inflammatory masses is by reducing drug density in e.g., CSF or other fluids, for drugs passed through a permeable membrane during delivery (which can reduce the size of any one droplet of the drug by the relatively small pore sizes of the permeable membranes).

[0135] As noted above, drug distribution patterns between the different compartments of the spinal canal may also be considered in connection with the present invention. In some instances, it may be desirable to place the infusion section or sections of the catheter in one or more selected locations in the spinal region.

[0136] The spinal canal is, however, not an open channel, but has several structures that divide the canal into separate channels. The dorsal nerve roots, ventral nerve roots, dentate ligaments, and septum posticum are typically present over the length of the spinal cord. They can act as barriers to even distribution of a drug around the circumference of the spinal cord. As a result, it may be desirable to locate an infusion section on a catheter in, e.g., a dorsal location, ventral location, etc. with respect to, e.g., the spinal cord.

[0137] For example, sensory signals, including pain signals, are transmitted into the spinal cord through the dorsal roots. The first synapse is located in the dorsal horn. It may be preferred, e.g., to locate an infusion section of a catheter on the dorsal side of the spinal cord to get the most drug (e.g., an analgesic drug) into the synapses in the dorsal horn. Motor signals are transmitted out through the ventral roots. Movement disorders may be controlled by enhancing the excitatory or inhibitory signals from the brain before the signals are transmitted to the ventral roots. In this case, it may be desirable to locate the catheter on the ventral side of the spinal cord and get the most drug into the ventral synapses.

[0138] Catheters of the present invention may, e.g., be inserted into the spinal region at a level below the end of the spinal cord and then threaded up to the desired level. The catheters may, however, be very limp, making it difficult or impossible to steer the catheter into a specific area of the spinal region. A guidewire may be used to stiffen the catheter during placement. The guidewire is then typically removed before the catheter is used to infuse drugs. The catheters of the present invention may include a guidewire lumen to receive the guidewire.

[0139] The guidewire may preferably have a bent tip so that the catheter and guidewire can be guided in a specific direction within the spinal region. Fluoroscopy or X-rays can be used to visualize the catheter during placement, and the guidewire rotated until the bend forces it to move in the desired direction. Catheters including guidewire lumens and/or bent tip guidewires may be described in, e.g., U.S. Pat. Nos. 4,811,743 (Stevens); U.S. Pat. No. 5,003,989 (Taylor et al.); and U.S. Pat. No. 6,512,957 B1(Witte).

[0140] Although the catheters, systems and methods of the present invention may be useful for infusing drugs to the CSF, there are other neurological applications where the present invention may be useful. One example would be to deliver drugs to other areas within the spinal region, for example, when the site of back pain can be localized to a disc, bone, muscle, or ligament in the spin, a mixture of a steroid and a local anesthetic can be delivered to reduce swelling and reduce pain. The infusion sections of catheters according to the present invention may preferably deliver drug to the entire structure, rather than delivering drug at a single point and depend on diffusion and convection to cover the entire area.

[0141] Another example would be delivering drugs into the brain. Functional areas in the brain are three-dimensional structures, not a single point. Clinical examples include delivering a chemotherapy agent to a tumor and delivering dopamine to the putamen for treatment of Parkinson's Disease. In yet another example, seizure activity in epileptic patients can be localized to a region in the thalamus or cerebral cortex. An anti-convulsant can be delivered to this region to terminate a seizure or to prevent further seizure activity. Again, a catheter with a permeable membrane may provide better organ coverage than delivering drug at a single point.

[0142] Yet another example would be a neurological disorder in a specific limb, such as an arm or leg. An example would be pain due to neuropathy caused by diabetes. The pain could be reduced by delivering a local anesthetic (and potentially a steroid) to a main trunk of the nerve that has been affected. The catheter with a permeable membrane could be surgically placed alongside the nerve, and infuse drug over a length of the nerve. The anesthetic may preferably cover a larger area of the nerve and be localized to the specific nerve, rather than deliver the drug at a point and depend on diffusion and convection to distribute the drug. FIG. 1C depicts a catheter placed next to a peripheral nerve in the arm. It should be recognized that these are only examples; other organs and disease states could also benefit from the use of this catheter.

[0143] Another drug distribution factor to consider in connection with the present invention is whether the drug is hydrophilic or lipophilic. Although not wishing to be bound by theory, it is theorized that hydrophilic drugs may have a wider distribution profile than lipophilic drugs. Accordingly, if it is desirable to reach a variety of levels of a spinal canal with a drug, it may be desirable to select and/or formulate a drug with hydrophilic properties. Alternatively, if it is desired to have a drug localized to a region around a particular level of the spinal cord, a drug having more lipophilic properties may be selected.

[0144] Drug distribution within the spinal canal may also be affected by controlling the temperature of the drug as delivered to the spinal canal. For example, heating the drug solution may make that solution more hypobaric (e.g., less dense) and/or cooling the drug solution may make it hyperbaric (e.g., more dense). FIG. 9 depicts a system in which the pump assembly 610 includes a thermal control device 660 to adjust the temperature of the drug solution before delivery to the catheter 620. In addition to or in place of thermal control device 660, the catheter 620 may include a thermal control device 662. Suitable thermal control devices may be, e.g., electrical resistance heaters, Peltier devices, etc.

[0145]FIG. 10 is a schematic diagram of another drug delivery system according to the present invention. The system 700 includes a pump assembly 710 (preferably implantable), catheter connection port 712, and two reservoirs 714 and 715 (preferably implantable). The reservoirs 714 and 715 are connected to the pump assembly 710 through a reservoir switching valve assembly 770 that is capable of selectively connecting the reservoirs 714 and 715 to the port 712.

[0146] Also depicted in FIG. 10 is a controller 702 for operating one or more components of the system 700. The controller 702 may be, e.g., a microprocessor or other control device. The controller 702 is depicted as being operably connected to the pump assembly 710, reservoir switching valve assembly 770, an external density sensor 750, an internal density sensor 752, and a telemetry module 780. The controller 702 may be used to adjust the pump assembly 710 to, e.g., obtain a desired flow rate, back pressure, etc. In such a capacity, the pump assembly 710 and controller 702 may operate as a programmable pump assembly. Although controller 702 is depicted as a separate component, it will be understood that it could be incorporated into one or more of the components in the depicted system 700 (e.g., the pump assembly 710, etc.). Also, although pump assembly 710 is depicted as a single component, it will be understood that pump assembly 710 could include one, two, three, or more pump mechanisms that may be operated independently of each other.

[0147] The optional telemetry module 780 may be operatively connected to the controller 702 to provide for communication between one or more of the components in system 700 and a user, external programming device, etc. Telemetry control devices, systems and methods that may be used in connection with the present invention may be described in, e.g., U.S. Pat. No. 5,558,640 (Pfeiler et al.); U.S. Pat. No. 5,820,589 (Torgerson et al.); and U.S. Pat. No. 5,999,857 (Weijand et al.). Although telemetry module 780 is depicted as being connected to the controller 702, it will be understood that the telemetry module 780 may alternatively be connected directly to one or more of the components, e.g., the pump 710, mixing means 713, density sensors 750/752, reservoir switching valve assembly 770, etc. The telemetry control module 780 may provide for one-way or two-way communication.

[0148] An optional external density sensor 750 is depicted in connection with FIG. 10 as operably connected to the controller 702 of drug delivery system 700. The external density sensor 750 may preferably be implantable and may be used in a control loop to, e.g., provide density information such that a reservoir from which a drug is to be delivered can be selected. If implanted, it may be preferred that the external density sensor 750 be located within the fluid into which the drug or drugs are to be delivered, e.g., the CSF of a patient.

[0149] An optional internal density sensor 752 is also depicted in connection with FIG. 10 and may be used to, e.g., sense the density of the drug solution as delivered to the catheter connection port 712. Such an internal density sensor 752 may be used in, e.g., a closed loop control system in which, e.g., the density of the CSF of the patient is determined and a selected density for the drug solution to be delivered to the patient is determined. The drug solution can then be formulated from, e.g., the fluids in reservoirs 714 and 715. Before the drug solution is delivered to the patient, however, its actual density can be measured using internal density sensor 752 such that adjustments can be made (if needed) to provide a drug solution with the desired density. Such a method/system may be described as a closed loop control system/method.

[0150] Alternatively, the system may be operated in an open loop configuration. In one embodiment, the external density sensor 750 may be provided to determine the density of, e.g., the CSF and provide that information to controller 702 which can then adjust the density of the drug solution using, e.g., reservoir switching valve assembly 770. In such an open-loop system/method, an internal density sensor 752 may not be provided, with the density of the drug solution being calculated on, e.g., known or expected values of the different components in reservoirs 714 and 715.

[0151] In another embodiment of an open-loop control system/method, only an internal density sensor 752 may be provided such that the actual density of the drug solution delivered to the catheter connection port 712 can be measured and adjusted based on a desired density.

[0152] Still other embodiments of open-loop control systems and methods may be envisioned in connection with the present invention.

[0153] The system 700 may also preferably include means for mixing 713 if it is desired to mix the fluids within the reservoirs 714 and 715. The means for mixing may take any suitable form and be located in any suitable location. For example, the means for mixing 713 may be located within the valve assembly 770, pump 710, port 712 or at any other location. As discussed herein, the means for mixing 713 may take a variety of forms including both active mixing devices (e.g., mechanical agitators)and passive mixing devices (e.g., mixing chambers, static mixers, etc.). The means for mixing 713 may preferably be connected to the controller 702 as shown if control over the means for mixing 713 is desired or required during operation.

[0154] Yet another alternative drug delivery system according to the present invention is depicted in FIG. 11. In many respects, the system 800 may be similar to system 700 of FIG. 10. System 800 does, however, preferably include a lumen switching valve assembly 890 located between the catheter 820 and the drug delivery system 800 such that output from the system 800 can be directed into the appropriate lumen 826 a and/or 826 b of catheter 820. The lumen switching valve assembly 890 and the system 800 may preferably be operably connected to, e.g., a controller located within system 800 (as described in connection with, e.g., system 700 above). Also, the system 800 may preferably include a pump assembly that includes two or more independent pump mechanisms to deliver drugs to the different lumens in catheter 820 independently.

[0155] In some situations, it may be desired to infuse a drug to multiple locations that are not collinear such that they cannot be reached by a single, unbranched catheter. As an example, it may be desired to infuse the same drug into both hemispheres of the brain. To accomplish such a method, a catheter may be used that includes one or more forks (e.g., a “Y”) at which the catheter splits into two or more separate branches. One example of such an embodiment is depicted in FIG. 12. The catheter 920 splits into branches 920 a and 920 b at fork 923.

[0156] Branch 922 a includes two infusion sections 927 a and 927 b located along the elongated body of the branch 922 a. As a result, infusion section 927 b is located between the proximal end 922 of the catheter and the other infusion section 927 a. Although only two infusion sections are shown along branch 920 a, it will be understood that three or more infusion sections could be provided along the branch 920 a or in-line with each other from the proximal end 922 to the distal end 924 a of branch 920 a. In some embodiments, it may be possible that an infusion section could be located along the length of the catheter 920 between the fork 923 and the proximal end 922, with one or more infusion sections located along one or both of the branches 920 a and 920 b.

[0157] Also, while catheter 920 includes only one fork and two branches, it should be understood that catheters of the present invention and systems/methods using them could include more than one fork and/or that each fork could include two or more branches.

[0158] One or more of the infusion sections on a branched catheter may preferably include a permeable membrane as described in connection with other embodiments herein. The permeable membranes used in the various infusion sections may have the same characteristics or they may be different. For example, the permeable membrane in each infusion section may have the same pore size if it is desired to have an equal amount of drug be infused from each infusion section. Sometimes, however, it may be desired to distribute different amounts of drug to two or more of the infusion sections. To do so, for example, the pore size of the permeable membranes in the different infusion sections could potentially be selected to provide the desired relative distribution. For example, a larger pore size could be expected to allow more drug to pass through the membrane, while a smaller pore size could be expected to allow less drug to pass through the membrane.

[0159] The branched catheter 920 could be designed with a single lumen that splits at fork 923 to service the infusion sections 927 a and 927 b on branch 920 a and infusion section 927 c on branch 920 b. Alternatively, however, multiple lumens could be provided to service each of the infusion sections 927 a, 927 b, and 927 c separately. Such a configuration could allow for the delivery of different drug solutions to the different infusion sections 927 a, 927 b, and 927 c as discussed herein with respect to multiple lumen catheters that are not branched. In still another variation, one infusion section could be serviced by a first lumen and two or more infusion sections (on the same or different branches) could be served by a common lumen (that splits if the commonly-served infusion sections are located on different branches.

[0160] The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. All publications mentioned herein are incorporated by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed.

[0161] As used herein and in the appended claims, the singular forms “a,” “and,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a drug” includes a plurality of drugs and reference to “the lumen” includes reference to one or more lumens and equivalents thereof known to those skilled in the art.

[0162] Unless otherwise indicated, all numbers expressing measurements, pore sizes, etc. used in the specification and claims are to be understood as preferably being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0163] Illustrative embodiments of this invention are discussed and reference has been made to possible variations within the scope of this invention. These and other variations and modifications in the invention will be apparent to those skilled in the art without departing from the scope of the invention, and it should be understood that this invention is not limited to the illustrative embodiments set forth herein. Accordingly, the invention is to be limited only by the claims provided below and equivalents thereof. 

1. A drug delivery system comprising: a drug delivery apparatus comprising a pump assembly and two or more reservoirs operably connected to the pump assembly; a catheter connection port adapted to attach a catheter to the drug delivery system; and means for mixing fluids from at least two reservoirs of the two or more reservoirs at or before delivering the fluids to the catheter connection port.
 2. The system of claim 1, further comprising an implantable density sensor operably connected to the drug delivery apparatus.
 3. The system of claim 2, further comprising a telemetry module operably connected to the density sensor.
 4. The system of claim 2, wherein the density sensor is operably connected to the drug delivery apparatus, whereby a mixed fluid having a selected density can be obtained based on a density measured by the density sensor.
 5. The system of claim 1, wherein two reservoirs of the two or more reservoirs contain different fluids.
 6. The system of claim 5, wherein the different fluids comprise different densities.
 7. The system of claim 1, wherein a first reservoir of the two or more reservoirs contains a first fluid comprising a low density, a second reservoir of the of the two or more reservoirs contains a second fluid comprising an intermediate density, and a third reservoir contains a third fluid comprising a high density.
 8. The system of claim 7, wherein the second fluid comprises a drug.
 9. The system of claim 8, wherein the first fluid and the third fluid are substantially free of the drug.
 10. The system of claim 7, wherein at least two fluids of the first fluid, the second fluid, and the third fluid comprise the same drug.
 11. The system of claim 1, wherein two reservoirs of the two or more reservoirs contain the same drug in two different drug solutions having different densities.
 12. The system of claim 1, further comprising a thermal control device for controlling the temperature of the drug.
 13. The system of claim 1, wherein the pump assembly comprises an implantable pump assembly, and wherein the two or more reservoirs comprise implantable reservoirs operably connected to the implantable pump assembly, and further wherein the means for mixing comprises implantable means for mixing.
 14. A drug delivery system comprising: a drug delivery apparatus comprising a pump assembly and one or more reservoirs operably connected to the pump assembly; a catheter connection port adapted to attach a catheter to the drug delivery system; and a thermal control device for controlling the temperature of the drug.
 15. The system of claim 14, wherein the thermal control device controls the temperature of the drug before the drug is delivered to the catheter connection port.
 16. The system of claim 14, wherein the thermal control device controls the temperature of the drug after the drug passes through the catheter connection port.
 17. The system of claim 16, wherein the thermal control device is located within a catheter connected to the catheter connection port.
 18. The system of claim 14, further comprising an implantable density sensor operably connected to the drug delivery apparatus.
 19. The system of claim 18, further comprising a telemetry module operably connected to the density sensor.
 20. The system of claim 18, wherein the density sensor is operably connected to the drug delivery apparatus, whereby a fluid having a selected temperature can be obtained based on a density measured by the density sensor.
 21. The system of claim 14, wherein the pump assembly comprises an implantable pump assembly, and wherein the one or more reservoirs comprise implantable reservoirs operably connected to the implantable pump assembly, and further wherein the thermal control device comprises an implantable thermal control device.
 22. A method of adjusting the density of a drug solution to be delivered to an internal body location of a patient, the method comprising: determining a selected density for the drug solution; formulating the drug solution from two or more components to obtain the selected density for the drug solution; and infusing the drug solution to an internal body location at a continuous rate of no more than 50 ml per hour for a period of five minutes or more.
 23. The method of claim 22, wherein the infusing is performed for a period of at least 8 hours within a twenty four hour period.
 24. The method of claim 22, where the infusion is performed for a duty cycle of at least 25% within a time period of 8 hours or more.
 25. The method of claim 24, wherein the duty cycle is at least 50% or more.
 26. The method of claim 25, wherein the time period is 12 hours or more.
 27. The method of claim 22, wherein determining the selected density comprises determining the density of the cerebrospinal fluid of a patient.
 28. The method of claim 27, wherein determining the density of the cerebrospinal fluid comprises locating a density sensor within the cerebrospinal fluid of a patient in vivo.
 29. The method of claim 27, wherein determining the density of the cerebrospinal fluid comprises measuring the density of the cerebrospinal fluid after removing the cerebrospinal fluid from the patient.
 30. The method of claim 22, wherein formulating the drug solution comprises formulating the drug solution outside of the body of the patient.
 31. The method of claim 22, wherein formulating the drug solution comprises formulating the drug solution within the body of the patient.
 32. The method of claim 31, wherein the two or more components are obtained from two or more reservoirs implanted within the patient.
 33. The method of claim 22, further comprising delivering the drug solution to the patient.
 34. The method of claim 33, further comprising obtaining feedback regarding efficacy of the drug solution after delivering the drug solution to the patient.
 35. The method of claim 34, further comprising adjusting the density of the drug solution based on the feedback.
 36. A method of adjusting the density of a drug solution to be delivered to an internal body location of a patient, the method comprising: determining a selected density for the drug solution; and controlling the temperature of the drug solution to increase or decrease the density of the drug solution to reach the selected density.
 37. The method of claim 36, further comprising infusing the drug solution to an internal body location at a continuous rate of no more than 50 ml per hour for a period of five minutes or more.
 38. The method of claim 37, wherein the infusing is performed for a period of at least 8 hours within a twenty four hour period.
 39. The method of claim 37, where the infusion is performed for a duty cycle of at least 25% within a time period of 8 hours or more.
 40. The method of claim 39, wherein the duty cycle is at least 50% or more.
 41. The method of claim 40, wherein the time period is 12 hours or more.
 42. The method of claim 36, wherein determining the selected density comprises determining the density of the cerebrospinal fluid of a patient.
 43. The method of claim 42, wherein determining the density of the cerebrospinal fluid comprises locating a density sensor within the cerebrospinal fluid of a patient in vivo.
 44. The method of claim 42, wherein determining the density of the cerebrospinal fluid comprises measuring the density of the cerebrospinal fluid after removing the cerebrospinal fluid from the patient.
 45. The method of claim 36, wherein controlling the temperature of the drug solution comprises heating the drug solution within a catheter used to deliver the drug solution.
 46. The method of claim 36, wherein controlling the temperature of the drug solution comprises heating the drug solution before delivering the drug solution to a catheter used to deliver the drug solution to the patient.
 47. The method of claim 36, wherein the drug solution is obtained from one or more reservoirs implanted within the patient.
 48. The method of claim 36, further comprising delivering the drug solution to the patient.
 49. The method of claim 48, further comprising obtaining feedback regarding efficacy of the drug solution after delivering the drug solution to the patient.
 50. The method of claim 49, further comprising adjusting the density of the drug solution based on the feedback. 